1. Field of the Invention
The present invention relates to a hydrous composition containing microcapsules and a process for the production of microcapsules. More specifically, it relates to a hydrous composition containing microcapsules, in which useful components are protected stably by microencapsulation and the effect of the useful components can be exhibited by dissolution of the microcapsules when diluted with water during use.
2. Description of the Related Art
Methods for stably protecting useful components by microencapsulation in aqueous compositions are described in, for example, Japanese Unexamined Patent Publication (Kokai) No. 49-453, Japanese Patent Publication (Kokoku) No. 50-25011, German Patent No. 1268316, U.S. Pat. No. 4,115,316. According to these methods, useful components are coated with a water-insoluble coating agent or useful components are coated with a water-soluble coating agent followed by application of chemical treatment on the coating agent for insolubilization to obtain water-insoluble microcapsules, before being formulated into a hydrous composition. However, when this composition is used, it is necessary to destroy the microcapsules by the application of a mechanical force, whereby there is involved the problem that not only a long time is required before destruction of the microcapsules, but also the useful components cannot be utilized 100% effectively due to the difficulty in destroying uniformly all of the microcapsules. Further, since a mechanical force is required during use, the scope of usage has been itself limited.
On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 50-3105 proposes to formulate water-soluble microcapsules in an anhydrous shampoo or rinse composition. However, since the composition is made anhydrous, there are problems such that useful water-soluble components become insolubilized to make formulation difficult or that the price of the composition becomes higher, and its uses have been also limited.
Microcapsules have excellent functions such that liquid or gaseous materials can be handled as solid materials, that substances readily reactive with each other can be separated, that substances can be protected from surrounding environment, and that the conditions for releasing the core material can be controlled. Various processes have been known for the preparation of such microcapsules. Among them, the process for production of microcapsules by utilization of liquid-liquid phase separation (coacervation) is an industrially useful production process, since excellent microcapsules having a high coating ratio and dense coating can be produced with a high efficiency.
However, in the prior art, when attempts are made to produce microcapsules with a wall material of a polyvinyl alcohol according to this process, a practically useful microcapsule cannot be obtained, because of the difficulty in forming the separated phase endowed with the physical properties demanded for capsule formation. For example, when microcapsules are produced according to the simple coacervation method by an addition of an electrolyte to an aqueous polyvinyl alcohol solution, the separated phase fails to enclose the capsule core material or, if the capsules are formed, the capsules became agglomerated into a coarse mass.
Under such circumstances, Japanese Examined Patent Publication (Kokoku) No. 47-51714 proposed a process for microencapsulation according to the simple coacervation method with the use of a complicated bound product of a polyvinyl alcohol and a polyhydroxy aromatic substance as the wall material. However, the polyhydroxy aromatic substance has a reducing ability and a strong chemical activity, and has the properties of readily binding or reacting with a metal or compounds having an amino, hydroxyl, aldehyde group, etc., and therefore the core material may be undesirably denatured or deteriorated depending on the capsule core material employed. Also, the presence of a polyhydroxy aromatic substance posed a problem of discoloration of the capsules by air, light, or metal ions. Japanese Examined Patent Publication (Kokoku) Nos. 47-51712 and 47-51713 also teach the use of alkyleneglycol cyclic borates instead of the polyhydroxy aromatic substance mentioned above. However, these additives have the same problems mentioned above.